Fiber Saturation Point Research Articles

Moisture content estimation of green softwood logs of three species based on measurements of flexural vibration

The moisture contents of sugi (Cryptomeria japonica), todomatsu (Abies sachalinensis) and hinoki (Chamaecyparis obtusa) logs were estimated using a method of moisture content estimation proposed in our previous study. In the course of estimation, it was revealed that the regression line of the correlation between specific dynamic Young’s modulus (E/ρ) and tangent loss (tan δ) of green wood was different from that of moisture-conditioned wood and showed species dependency, both of which are not previously reported. Regression lines at the fiber saturation point (FSP) were constructed for each species by measuring E/ρ and tan δ from the flexural vibration of green small specimens and correcting the E/ρ values at their own moisture contents into E/ρ values at the FSP. The correlation of green wood in this study was different from that reported in previous studies of moisture-conditioned wood near the FSP. The correlations of sugi and hinoki were similar, whereas those of sugi and todomatsu were different despite no previous report of species dependency in air-dried wood. The moisture contents 86 logs (not those used to prepare small specimens) were estimated using regression lines of each species. The standard deviation of the difference between the estimated moisture content and the measured moisture content was 15.7%. A systematic error of 25.9% in moisture content was attributed to the different methods of specimen support used for small specimens and logs.

Pulp delignification and refining: impact on the supramolecular structure of softwood fibers

The effect on softwood fiber wall nanostructure of kraft cooking, oxygen delignification and refining was evaluated by X-ray scattering. A recently developed simulation method for modelling small angle X-ray scattering (SAXS) data was used to estimate the apparent average sizes of solids (AAPS) and interstitial spaces in the fiber wall (AACS). Fiber saturation point and wide angle X-ray scattering were also used to calculate the pore volume in the fiber wall and the crystallite size of the fibril, respectively. The experimental modelled SAXS data was able to give consistent values for each kraft-cooked and oxygen-delignified pulp. Kraft delignification seems to have the major influence on the fiber nanostructure modification, while oxygen delignification has little or no significant impact even for different kappa numbers. The particle sizes values were more stable than the cavities sizes and no significant differences were seen between different delignification processes, refining or delignification degree. Pulps evaluated after PFI-refining, showed an increase in the fiber wall porosity evaluated by FSP and an increase in the interstitial spaces in the fiber wall, while the crystallite size and the particle sizes were very little or not affected at all.

Comparative research on the structure, chemistry, and physical properties of Turkey oak and sessile oak wood

The objective of this research was to establish comparatively some relevant features of Turkey oak and sessile oak wood, in order to better understand the drying behavior of these species. The analyzed samples were obtained from freshly harvested trees of the same age, originating from the Southern Sub-Carpathians. The microscopic analysis revealed that Turkey oak has larger earlywood pores than sessile oak. In heartwood, they are partly filled with tyloses for both species. The macroscopic analysis showed that Turkey oak wood has a much lower proportion of heartwood (only 50%) compared to sessile oak (90%). The comparative FTIR analysis of the two species showed similar qualitative chemical composition, but also some differences between sapwood and heartwood regarding the relative proportion of the main constituents, and very likely in the structure of lignin. High amounts of extractives were found in Turkey oak sapwood (5.34% in cold water, 7.77% in hot water, and 21.60% in NaOH 1%), close to the values obtained in sessile oak heartwood. The research also revealed that the Turkey oak sapwood and heartwood have statistically similar values of oven-dry density, shrinkage coefficient, fiber saturation point, while in sessile oak, the values are clearly higher in the heartwood.

The influence of loading speed on the bending strength of beech (Fagus sp.) and birch (Betula sp.) wood

The influence of loading speed on the bending strength of beech (Fagus sp.) and birch (Betula sp.) wood The subject of this paper was to investigate the effect of loading speeds from 20 mmˑmin-1 to 200 mmˑmin-1 on the flexural strength and deformation of beech (Fagus sp.) and birch (Betula sp.) wood with moisture content close to the absolutely dry state and fibre saturation point. A GOM Aramis measuring system, operating with Digital Image Correlation (DIC) technology, was used in the study to record the displacement and deformation of the elements in real time. The results obtained for flexural strength, flexural modulus and the amount of deformation observed showed a relationship between material properties and loading rate. At higher moisture content, the bending strength and modulus of elasticity decreased with increasing deflexion. The highest bending strength and modulus of elasticity were achieved by the tested wood species at a loading rate of 200 mmˑmin-1. Beech wood, compared to birch wood, showed higher bending strength and modulus of elasticity. Images obtained by means of DIC revealed, at moisture contents close to the dry state, a symmetrical distribution of compressive and tensile stresses relative to the neutral axis of the sample cross-section. At higher moisture contents, there was a significant asymmetry between the compressive and tensile stresses and an apparent shift of the neutral axis towards the tensile surface.

Permeability of wood impregnated with polyethylene wax emulsion in vacuum

Polyethylene wax (PEW) has emerged as a commonly used material for maintaining the quality of wood. The emulsification of solid PEW before being injected into wood can effectively overcome the shortcomings of the high-temperature melting and injection process of solid PEW. The permeability of Eucalyptus (Eucalyptus saligna) and Mongolian Scotch pine (Pinus sylvestris var. Mongolica) to PEW emulsion in vacuum environment was investigated using impregnation tests, and steaming pretreatment and microwave irradiation pretreatment were applied. The small particle size and low viscosity of the PEW emulsion, whose median particle size was 0.256 μm and viscosity was 52.2 mPa s (at 60 r/s), facilitated its penetration into the wood capillary system. The weight percent gain (WPG) of Eucalyptus and Mongolian Scotch pine post impregnation in vacuum was positively correlated with both the vacuum-holding time and the impregnation temperature, but after 60 min of impregnation the WPG of both wood species decreased significantly. Both pretreatment methods could substantially improve the wood permeability and effectively promote the penetration of the PEW emulsion into the wood. The maximum WPG was achieved when Eucalyptus and Mongolian Scotch pine were respectively steamed for 80 min and 120 min. There was an increase of 0.24 times for the former and an increase of 0.53 times for the latter compared to unpretreated wood. Both species exhibited the highest WPG after water immersion for 60 min (with average moisture content close to their fibre saturation point) and microwave irradiation for 30 s, which was respectively 0.28 and 0.75 times higher than that of unpretreated wood. There was a significant variation in WPG between the two species with the same pretreatment method. The relatively lower density and better-developed capillary system of Mongolian Scotch pine allowed more efficient penetration of PEW emulsion. It is recommended that, considering the time cost and practical enhancement, microwave irradiation should be given priority to when pretreating wood.

Effect of Alternate Drying Techniques on Cross-Laminated Timber after Exposure to Free-Water Wetting

Cross-laminated timber (CLT) panels are commonly used in mass-timber multistorey constructions due to their prefabrication, construction flexibility, environmental credentials and weight-to-strength ratio advantages compared to competing building materials. However, the long-term durability and service life of these mass timber panels require further understanding of their performance when exposed to free water. Wetting and drying trials were conducted by exposing Radiata pine (Pinus radiata) CLT sections to either free water (pooling on a single surface) or submerged water (all directions exposed) saturation, followed by either ambient or fan drying. The panels exposed to water pooling only reached MC above the FSP up to 40 mm of the panel depth. For submerged panels, the MC reached values above the fibre saturation point (FSP) at depths of 30 to 40 mm penetration on both panel faces. When comparing the ambient and fan-drying panel sections over the same time period, a less uniform MC profile was observed for the ambient drying, whereas the fan-dried panels fell below the FSP faster and with a more consistent MC profile. A complementary study was conducted on a standalone 3.0 × 3.0 m CLT room, where the room was wetted during a simulated pipe burst event. The moisture monitoring of wall and floor panels during fan drying of the room showed that an MC reduction from an excess of 40% to below 20% could be reached in less than 96 h for the panels’ surface; however, the middle sections of the panels dried slower than the surface sections. The CLT structure fan drying required a longer drying time than the CLT sections tested due to the closed sections (overlaps and connected faces) and a lower rate of airflow. The study of drying CLT sections highlighted the product reaching and maintaining MC higher than FSP points and the need for further drying applied to minimise long-term decay development. Further study is recommended to investigate the effects of closed sections (connected faces) and the duration of drying needed for semi-finished and finished buildings.

Digital image correlation method for detecting strain in wood drying process

Stress and strain monitoring is of great significance for wood drying. Using digital image correlation (DIC), this study measured displacement and strain changes during wood drying in real time. The results showed that when wood is dried below the fiber saturation point, the difference of the radial and tangential shrinkage ratio gradually increased. An analysis of tangential and radial shrinkage ratio revealed that in the early stage of drying, the tangential and radial shrinkage ratio was relatively flat; in the middle stage of drying, the shrinkage ratio began to gradually increase; and in the later stage of drying, the tangential shrinkage ratio was approximately twice as large as that in the radial direction. Further, regarding the tangential and radial strain distribution, the radial strain distribution was more scattered than that in the tangential direction. The radial strain distribution exhibited compressive strain on both ends of the specimen, and the tensile strain was in the center. The tangential strain distribution was tensile strain on the left side of the specimen and compression strain on the right. Overall, DIC is stable and reliable, and it can be used to monitor well the stress and strain changes during wood drying.

Comparison of Eucalyptus spp. wood quality in solar and conventional drying

The aim of the study was to compare the quality of sawn Eucalyptus spp. wood under solar and conventional drying, focusing on parameters such as drying rate, moisture gradient, drying stresses, and wood defects. For this purpose, a comparison was made between samples dried in a solar kiln and a conventional drying chamber. As a preliminary analysis, the specific gravity and initial moisture content of the wood were evaluated, and the quality and drying parameters of the wood were assessed both before and after the drying process. It was observed that the drying rate in the conventional chamber was twice as high above the fiber saturation point and four times higher in the diffusion phase compared to solar drying. Regarding the moisture gradient and defect index, there was no statistical difference between the two processes. However, the percentage of pieces with defects was significantly higher in conventional drying, as well as demonstrating higher drying stresses, which may hinder mechanical processing after water removal. Therefore, it can be concluded that solar drying presents a quality similar to conventional drying and can be a good alternative for drying processes.

Changes in Moisture Characteristics of Waterlogged Archaeological Wood Owing to Microbial Degradation

Studying waterlogged archaeological wood moisture characteristics can provide strong support for the safe dehydration and preservation of waterlogged wooden artifacts. Herein, six waterlogged archaeological wood samples with moisture contents of 154%–968% chosen from two ancient Chinese shipwrecks, Nanhai No. 1 and Changjiangkou No. 2, and six non-degraded modern wood samples of the relevant corresponding species were selected to study the moisture characteristics by low-temperature nuclear magnetic resonance (NMR) and the dynamic sorption of water vapor (DVS). It was found that the six waterlogged archaeological wood samples exhibited three deterioration states: slightly, moderately, and seriously deteriorated. Wood deterioration caused significantly increased fiber saturation point (FSP) values for waterlogged archaeological wood. This is mainly owing to changes in the pore size distribution of cell walls. Moreover, NMR is more accurate than DVS in obtaining FSP for severely degraded samples. Additionally, moisture content was positively associated with wood deterioration. Maximum water content (MWC), free water content, and bound water content exhibited an exponential relationship with the basic density (BD). The contribution of bound water in waterlogged archaeological wood was less than that of modern wood and decreased with deterioration.

Water in Wood: A Review of Current Understanding and Knowledge Gaps

Wood-water interactions are central to the utilization of wood in our society since water affects many important characteristics of wood. This topic has been investigated for more than a century, but new knowledge continues to be generated as a result of improved experimental and computational methods. This review summarizes our current understanding of the fundamentals of water in wood and highlights significant knowledge gaps. Thus, the focus is not only on what is currently known but equally important, what is yet unknown. The review covers locations of water in wood; phase changes and equilibrium states of water in wood; thermodynamics of sorption; terminology including cell wall water (bound water), capillary water (free water), fiber saturation point, and maximum cell wall moisture content; shrinkage and swelling; sorption hysteresis; transport of water in wood; and kinetics of water vapor sorption in the cell wall.

Investigation and modelling of the electrical charging effect in birch wood above the fibre saturation point (FSP)

Abstract Wood moisture content (MC) has a significant impact on all electrical properties of wood. Regarding the development of the (so-called polarization-type) wood moisture meter with the electrical charging effect for monitoring and controlling the wood drying process, it is of interest to expand the theoretical background of this type of novel wood moisture meter by means of modelling. Two mediums were selected for modelling – raw birch wood and, as a reference medium, birch liquid sap – into which two symmetrical carbon fibre measuring electrodes were inserted. In both mediums, direct current and alternating current were passed between electrodes at different electrode potentials. The electrical field and electrical response of the current-affected mediums were then measured and modelled in the time domain and frequency domain. The numerical results of modelling are comparable both in the time domain and frequency domain (i.e. if E = 1.8V, then Cs = 0.5 mF and C1,int = 0.7 mF). The concept of energetic chargeability (CHA(W)) of wood was defined and compared to conventional chargeability as defined by C. Schlumberger in 1913. Empirical dependencies of CHA(W) on electrode potential and primary energy W1 transmitted through the wood (sap) medium were found. In the frequency domain, frequency dependencies were found to distinguish between adsorption processes and mixed kinetics ranges in birch sap and in raw birch wood.

Effect of Samples Size on the Water Removal and Shrinkage of Eucalyptus urophylla × E. grandis Wood during Supercritical CO2 Dewatering

Eucalyptus urophydis E. grandis green wood with different lengths were dewatered using CO2 that was cyclically alternated between the supercritical fluid and gas phases. The results indicate that shorter specimens can be dewatered to below the fiber saturation point (FSP). There was no significant difference in the dewatering rate between the specimens of 20 and 50 mm in length. The dewatering was faster when the moisture content (MC) was over the FSP, leading to a greater gradient and a non-uniform distribution of moisture. The MC distributions in all specimens had no clear differences between in tangential and radial directions. Supercritical CO2 dewatering generated a different moisture gradient than conventional kiln drying. Most water was dewatered from the end-grain section of the wood along the fiber direction, but a small amount of water was also removed in the transverse directions. There was no deformation in the specimens when the MC was above the FSP.

Moisture Absorption Behavior of CP5 Composite Materials Used in Industry

In engineering practice, perhaps the most interesting aspect of woodworking deals with the relationship between wood and moisture. The plywood composite presents hygroscopicity characteristic, as the wood and reaction almost like a sponge, will gain or lose moisture from the air based upon the conditions of the surrounding environment. When the tree is in the green state, is first felled, it contains a very large amount of moisture existing in two different forms: as free water that is contained as liquid in the pores or vessels of the wood itself and as bound water, trapped within the cell walls. After that the wood is exposed to the air and immediately loose free water and the wood does not contract or otherwise change in dimension, it is in the state of drying and it is called the fiber saturation point. The moisture content in each piece of CP5 composite material is expressed as a percentage of the weight of the water and oven-dry weight of CP5 composite material. The moisture absorption depends on the wood type, density of wood and it is influenced by the environmental temperature, this is an aspect very important in the furniture industry. The moisture absorption test is generally used for quality control purposes and to measure the degradation of the quality for the wood and composite materials.

Dimensional stability and moisture-induced strains in spruce cross-laminated timber (CLT) under sorption/desorption isotherms

The paper presents a comprehensive experimental–numerical study on dimensional stability of spruce CLT panels and provides new insights into understanding the effect of mechanical properties of wood layers on moisture-induced strains. Deformations in Norway spruce CLT as well as their wood layers were studied in two orthogonal planes under sorption and desorption cycles. Coefficients of Moisture Expansion (CME), Coefficient of Moisture Contraction (CMC), as well as Coefficient of Thermal Expansion (CTE) were determined using dimensional measurements at 15° and 50℃. A 3-D nonlinear finite element (FE) model was developed to better understand the effect of glue and wood mechanical properties, as well as their CME and CTE on two CLT cross-sections. Unlike previous studies, the glue layers have been modelled as thin physical layers bonding wood layers. Hence, the effect of glue lines on the performance of CLT panels can be elucidated quantitatively. Results demonstrated good agreement between the FE model predictions of moisture-induced strains and the experimental data under both sorption and desorption isotherms when the wood moisture content is below fibre saturation point (FSB). Discrepancies between experiments and the model were noted at moisture contents above FSB. Such discrepancies may be attributed to measurement inaccuracies at small scale, the annual ring patterns, uncertainties in material properties, glue penetration into wood cell walls, as well as imperfect bonding at the glue lines. Results highlighted the significant effect of the mismatch between CTE and CME (or CMC) of wood in different directions on the development of stresses and consequently delamination, and perpendicular to grain failure in CLT panels subjected to extreme humidity levels.

Potential to use invasive plants in biomass energy production: A case study Prosopis juliflora in coastal wetlands of Sri Lanka

Prosopis juliflora is an invasive plant species rapidly expanding in the Asian and African continents. The invasion of P. juliflora in Bundala Ramsar Wetland (BRW) in Sri Lanka has created several biodiversity conservation issues. This study was conducted to assess the possibility of utilizing invasive P. juliflora as an alternative energy source. P. juliflora performed better than L. leucocephala for most evaluated fuelwood properties. Ash content was comparatively higher in P. juliflora than L. leucocephala. However, biomass to ash ratio of P. juliflora was significantly lower (<0.05) and the Fuel Value Index (FVI) of P. juliflora (3,276) was slightly lower than that of L. leucocephala (3,336), a non-significant difference. P. juliflora and L. leucocephala reached Fiber Saturation Point within 24 and 27 days of drying, respectively. Results show that 1 kg of P. juliflora would produce an estimated energy equivalent to 0.5 L of diesel and furnace oil and 5 kWh of electricity. As such, we recommend further study on harvesting and commercialization of P. juliflora as a potential wood energy source.

Influence of moisture content on the dynamic modulus of elasticity

Pinus forests are the second most planted in Brazil and the wood obtained from them is mainly used as structural elements in the civil construction sector. The Brazilian standard that deals with calculations of wooden structures projects recommends the use of wood in the range of 10% to 20% of moisture content. Thus, this study aimed to present an investigation about the influence of moisture content on the static modulus of elasticity (MOEst) of wooden beams by transverse vibration tests. The MOEst was evaluated by static bending tests and transverse vibration tests for various moisture content. The transverse vibration test was performed in a free condition using an accelerometer and an impulse hammer, and the dynamic modulus of elasticity (MOEd) was determined from the frequency of the first bending vibration mode. A total of 20 wooden beams were obtained from freshly cut Pinus spp. logs with initial high moisture content were used, with nominal dimensions of 5 cm × 10 cm × 200 cm (thickness × width × length). It was observed that the MOEd is also affected by moisture content according to the non-linear regression model. There were significant changes in the dynamic modulus of elasticity (MOEd) for the moisture contents (M) below 25% (near the fiber saturation point - FSP).

Influence of Timber Moisture Content on the Ultrasonic Wave Velocity Measurement of Tectona grandis L.F. and Cupressus lusitanica M. from Costa Rica

Ultrasound is a reliable non-destructive method commonly used to evaluate the state of a piece of wood. The effect of the moisture content (MC) on the timber wave velocity, which is different depending on the wood species, must be considered. MC adjustment factors are important if accurate and comparable results are to be achieved. Thus, the goal of this study is to define a model that allows obtaining the adjustment factor to predict the standard velocity (12% of MC (V12) from velocity obtained at different MC for two Costa Rican commercial species: Tectona grandis L.F (teak) and Cupressus lusitanica M. (cypress). This effect was studied on small clean specimens during the desorption stages, from the fiber saturation point to the oven-dry state, controlling the specimen’s mass and MC on 62 specimens. With this data, the rate of change in ultrasound velocity per MC was modeled. Thus, the applicability of already published moisture adjustment models for conifers and hardwood tropical species was proved. The results showed that the proposed model coefficients adjust better than the ones obtained from the wood science literature, which makes them suitable to describe ultrasound velocity in different moisture conditions (VH).

The effects of using different adhesive on the thickness swelling ratio of LVL produced from scotch pine

Most wood properties are affected by changes in moisture content below the wood fiber saturation point. In this study, the thickness swelling ratios of laminated veneer lumber (LVL) produced from Scotch pine (Pinus sylvestris L.) bonded by using polyvinyl acetate (PVAc), polymeric diphenyl methane diisocyanate (pMDI), and a mixture of them were evaluated. Thickness swelling of the samples was calculated after different waiting times under water. While the lowest thickness swelling ratio (1.65%) was determined from bonding with PVAc 92%- pMDI 8%, for 2 hours, the highest thickness swelling ratio (6.35%) was observed from bonding with PVAc 98%- pMDI 2% adhesive for 96 hours. As a result, adding pMDI to the PVAc adhesive reduced the rate of swelling of the test specimens. For this reason, the material can be used potentially in wet or humid places.

Discrimination between softwood and hardwood based on hemicellulose content obtained with portable nuclear magnetic resonance

Wood is a hygroscopic material that can reach an equilibrium moisture content when ambient temperature and relative humidity are constant. Moisture affects all properties of wood, as well as its preservative treatment. The hygroscopic behavior of wood can be attributed to the hydroxyl groups of its constituents. Since hemicellulose shows the greatest water affinity, it can be considered the main responsible for the ingress of water into the wood mass. Below the fiber saturation point, wood moisture is only stored in the cell walls. Proton Nuclear Magnetic Resonance (NMR) is a relative method used for the evaluation of moisture content distribution in wood and NMR relaxation is an excellent tool to study the hygroscopic behavior of different woods below the fiber saturation point. This work aimed to test the hypothesis of discriminating among softwoods and hardwoods of different botanical species and identifying further sub-clusters of woods based on the NMR proton spin–spin (T2) and spin–lattice (T1) relaxation times of their cell wall water in the hygroscopic moisture range. Importantly, the study was performed using a portable low-cost NMR instrument with which it is possible to investigate wood samples of any size. The main result of this study was that at RH = 94% the relaxation time T2,2, associated with the cell wall bound water, can be used as a marker to discriminate among softwoods and hardwoods.Graphical abstract

Influence of Moisture Content on Cutting Parameters and Fracture Characteristics of Spruce and Oak Wood

The objective of this study was to determine the effect of the moisture content on cutting parameters and fracture characteristics of spruce and oak wood. Samples of Norway spruce (Picea abies (L.) H. Karst.) and English oak (Quercus robur L.) were dried to required moisture content and then used for the machinability test on circular sawblade machine. Results indicate that cutting force and feed force increase with increasing moisture content up to the fiber saturation point (FSP). When the moisture content increases above the FSP, the minimum values of cutting and feed force are achieved. Based on performed experiments, the fracture toughness and shear yield strength were derived. Fracture toughness decreases with increasing moisture content. The minimum values of fracture toughness are achieved at the moisture content level above the FSP. Shear yield strength decreases linearly with increasing moisture content: the decrease is up to 17 % compared to samples with moisture content at the FSP. Based on calculated results, the influence of moisture content and wood species on cutting and fracture characteristics was discussed.